Chem 112 Dr. Kevin Moore

Chem 112 Dr. Kevin Moore

Gas Liquid Solid

Polar Covalent Bond Partial Separation of Charge Electronegativity: H 2.1 Cl 3.0 H Cl δ + δ - Dipole Moment measure of the net polarity in a molecule Q Q magnitude of charge r distance between charges r

Consider H 2 O O H H Dipole Moment is the net of all bond dipoles N H H H

Non-polar molecules have no net dipole Even if individual bonds have dipoles H C H H H No Net Dipole!

Measured in Debye Coulomb-meters Q electron = 1.60 x 10-19 Coulomb = -1 For an electron at r=100 pm 160. 10 C 100. 10 19 10 m 1 Debye 3336. 10 30 Cm 480. D

Compound Dipole Moment (D) NaCl 9.00 CH3Cl 1.87 H2O 1.85 NH3 1.47 CO2 0 CCl4 0

Determined Experimentally Use to determine ionic character of bond % ionic Observed Ionic 100%

Calculate the % Ionic Character of H-Cl if the bond length is 127 pm and µ=1.03 D. e 127 pm 480. D 610. 100 pm D % Ionic 103. 610. D D 100% 16. 9 %

Calculate the % Ionic Character of HF if µ=1.82 D and the bond length is 92 pm. Draw the Lewis Structure and Dipole Moment. e 92 pm 480. D 44. 100 pm D % ionic 182. D 44. D 100% 414. % H-F

Draw Dipole Moments along the bond Show 3D structure Draw the Lewis Structure and Dipole Moment for Methanol (CH 3 OH) H H C O H H

Solid and Liquid Phase implies a binding force Often called van der Waals forces Electrical in nature Ion-Dipole Interaction between a molecule and a charged ion O H H O H H

Strength of interaction Size Charge

Weak Force of interaction between dipoles Only relevant when molecules are very close together O S O O S O O S O

Orientation of Polar Molecules in a Solid

Strength of interaction is a function of dipole moment Substance Molar Mass Dipole Moment (D) Boiling Point (K) CH3CH2CH3 44.10 0.1 231 CH3OCH3 46.07 1.3 248 CH3Cl 50.49 1.9 249 CH3CN 41.05 3.9 355

Benzene (µ=0) Boiling Point = 80.1 C Melting Point = 5.5 C H C H C C H H C C C H H

1000 Instantaneous asymmetric distribution of charge 800 Causes a distortion in a molecule closeby ALL 600 substances experience LDF Boiling Pt 400 Melting Pt Substance Melting Point (K) Boiling Point (K) 200 F2 53.5 85.0 Cl2 0 172.2 238.6 Br2 38 265.9 71 160 254 331.9 I2 386.7 457.5

Non-polar compounds interact through random induced dipoles Electron Polarizability

Generally become stronger as molar mass and surface area increase n-pentane vs. neo-pentane

Interaction between a hydrogen bonded to a high EN atom (N, O & F) and unshared electrons (lone pairs) on another high EN atom. N O H H H H H O H H N H H H

Stronger interaction than dipole-dipole Through space interaction

Decreasing Molar Mass Decreasing Boiling Point

Summary Force Strength Effect Example Dispersion (LDF) Very Weak Depends on MW CCl4, C6H6, All Substances Dipole-Dipole Weak Solubility, BP, MP SO2, CH3COCH3 H-bonding Moderate BP, MP, 3D Structure H2O, NH3, Organic Acids, Organic Bases Ion-Dipole Strong Solubility

Draw Lewis Structure No Dipole? Yes LDF No Hydrogen Bonding? Yes Dipole-Dipole LDF H-Bonding LDF

Hydrocarbons are non-polar C 3 H 8 Symmetric molecules with no lone pairs on the central atom are non-polar Tetrahedral (CCl 4 ) Trigonal Planar (SO 3 ) Linear (CO 2 ) Different atoms connected to central atom is always polar CH 2 F 2 CH 3 COCH 3

Viscosity Measure of a liquid s resistance to flow Dependent on intermolecular forces

Resistance of a liquid to spreading out Least Surface Area Sphere

Capillary Action Interaction between a liquid and a porous solid in a narrow passage

Symbol Name Beginning Phase Ending Phase ΔH fus Fusion (Melting) Solid Liquid -ΔH fus Freezing Liquid Solid ΔH vap Vaporization Liquid Gas -ΔH vap Condensation Gas Liquid ΔH sub Sublimation Solid Gas -ΔH sub Deposition Gas Solid

Measure of disorder in a system Increases solid --> liquid --> gas 2 nd Law of Thermodynamics A closed system will undergo changes which increase the entropy of the system ΔS

Gibbs Free Energy G H T S ΔG<0 spontaneous ΔG>0 non-spontaneous ΔG=0 equilibrium Phase changes are equilibrium conditions

Process Enthalpy (ΔH) Entropy (ΔS) Free Energy (ΔG=0) Fusion >0 >0 Melting Point Vaporization >0 >0 Boiling Point Sublimation >0 >0 Situational Freezing <0 <0 Melting Point Condensation <0 <0 Boiling Point Deposition <0 <0 Situational

Strong intermolecular forces High Heat of vaporization

To break apart substances Requires Energy Increases Disorder Favorable when temp allows ΔS to dominate ΔG To organize substances Releases Energy Decreases Disorder Favorable when temp allows ΔH to dominate ΔG G H T S

Calculate the boiling point of water if the ΔH vap =40.67 kj/mol and ΔS vap =109 J/K-mol. Boiling is a phase change T H S 40670 J / mol 109 J / K mol 373 K T 100 C

Molar Heat Capacity amount of heat required to heat 1 mole of a substance by 1 C Specific Heat Capacity amount of heat required to heat 1 g of a substance by 1 C

Heat from -10 C to 110 C -10 0 Temperature ( C) 100 C ice = 36.5 Jmol -1 C -1 C H2O = 75.3 Jmol -1 C -1 C steam = 33.6 Jmol -1 C -1 ΔH vap = 40.67 kjmol -1 ΔH fus = 6.01 kjmol -1 0.365 6.37 13.9 54.6 54.9 Heat Added (kj)

#1 Warming the ice q 365. J ( 1 mol)( 10. 0 C) 365 J molc #2 melting the ice kj q 6. 01 ( 1 mol) 6010 J #3 warming the water fus mol q 75. 3 J ( 1 mol)( 100. C) 7530 J molc #4 vaporizing the water kj q 40. 67 ( 1 mol) 40670 J vap mol

#5 Heating of steam Total Heat J q 336. ( 1 mol)( 10. 0 C) 336 J steam molc q q q q q q tot ice fus water vap steam q 365 J 6010 J 7530 J 40670 J 336 J tot q 54911 J 54. 9 kj tot

Pressure of a liquid on a closed container Depends on Temperature All Liquids and many solids # of molecules Kinetic Energy ΔH vap

Passing of a liquid to a vapor without being at the boiling point Liquid cools as evaporation occurs

Vapor Pressure of a liquid can be used to derive the relationship Clapeyron Relationship dp dt PH RT vap 2

Boiling Point Temperature at which the vapor pressure is equal to atmospheric Pressure Integrating Liquid Vapor Relationship Claussius-Clapeyron Equation ln P vap H vap R 1 T C

P(mmHg) vs. T(K) 800.0 H 2 O 600.0 400.0 200.0 0.0 250.0 300.0 350.0 400.0 Pvap T 1/T Ln P vap 4.9 274 0.00365 1.59 13.5 289 0.00346 2.60 33.3 304 0.00329 3.51 74.5 319 0.00314 4.31 154 334 0.00300 5.04 296 349 0.00287 5.69 536 364 0.00275 6.28 760 373 0.00268 6.63

Plot ln P vap vs. 1/T 7 ln P vs. 1/T 6 5 4 3 2 1 0 0.002 0.0025 0.003 0.0035 0.004

Using equation ln ln ln P P vap 1 P H R vap 1 T Hvap Hvap ln P R 1 T R 1 2 1 T2 Hvap 1 Hvap 1 ln P R T R T 1 2 ln P P 1 C 2 1 H 1 1 vap R T T 2 2 1

Calculate the ΔH vap of ethanol, if the boiling point is 78.4 C and it has a P vap =100. mmhg at 34.7 C. T 1 =78.4 = 351.55 K T 2 =34.7 = 307.85 K P 1 =760. mmhg P 2 =100. mmhg ln 760 H vap 1 1 100 8. 314 307. 85 35155. J mol K 2028. H vap 8314. J mol K 4. 038 10 4 H 41800 J kj vap mol 418. mol

The normal boiling point of water is 100.0 C. What is the vapor pressure at 58.5 C if ΔH vap =40.67 kj/mol? ln760 40670 1 1 ln J mol x 8. 314 33165. 37315. J mol K ln x 4892 3353. 10 6. 633 4 ln x 4. 993 x 147 mmhg

Hydrogen Bonding Density of Water Specific Heat Density

Crystalline Solids Amorphous

Crystalline Solids form repeating cells

d represents the edge of a unit cell Packing Methods Coordination # Lattice Points Simple Cubic

Body Centered Cubic Packing Face-Centered Cubic Packing Hexagonal Closest Packing

Closet Packing: Hexagonal and Cubic hexagonal cubic

Shared by 8 unit cells Shared by 4 unit cells Shared by 2 unit cells

Simple Cubic Atomic radius d r 2r d 2

Body-Centered r 3 d 4

Face-Centered r d 8

Silver crystallizes in a face-centered (FCC) unit cell (cubic closest packing). If the edge length is 407 pm, what is the radius of Ag? r 407 pm 8 144 pm

Nickel has an edge length of 352.4 pm. If it is FCC, what is its density? d D 3524. 10 8 cm V d (. 3524 10 cm) 4. 376 10 cm m V FCC 4 atoms 4 atoms 3 8 3 23 3 1 mol 6. 022 10 23 atoms 58. 69 g 1 mol 3898. 10 22 g D 22 (. 3898 10 g) 4. 376 10 cm 23 3 8909. g cm 3

Titanium crystallizes in a BCC format. If the radius of a Ti atom is 144.8 pm, what is its density? 8 4(. 1448 10 cm) d 3 D m V BCC 2 2 atoms 3344. 10 8 cm V d (. 3344 10 cm) 3739. 10 cm atoms 3 8 3 23 3 1 mol 6022 10 atoms 23. 47. 87 g 1 mol 1590. 10 22 g D 22 (. 1590 10 g) 3739. 10 cm 23 3 4252. g cm 3

Cannot see atoms X-Rays can be used to determine crystal structure William Bragg Bragg Equation n=integer λ=wavelength Θ=angle of X-ray to crystal Used to determine atomic distances Usually measure in pm (10-12 m) d n 2sin

Energy required to break ionic solid into gas ions Solubility Melting Point

Intermolecular forces Ionic Crystals Ionic compounds High Lattice Energy

NaCl crystallizes in a face centered unit cell with an edge length of 564 pm. What is the density? Cell Contains: 4 Na + & 4 Cl - ions 4 Na 1 mol 6. 022 10 23 atoms 22. 99 g 1 mol 1527. 10 22 g 4 Cl 1 mol 6. 022 10 23 atoms 3545. g 1 mol 2. 355 10 Total Mass: 3.882 x 10-22 g V d (. 564 10 ) 179. 10 cm 3 8 3 22 3 22 g D D 3882. 10 179. 10 217. 3 g cm 22 g cm 22 3

Allotropes Different forms of substance in identical physical state Phosphorus Carbon Silicon

Plot of phases for Pressure vs. Temperature SuperCritical Fluid Solid Liquid Gas

Triple Point Critical Temperature Critical Pressure Slope of solid/liquid line